Most web users would agree that entering text into CAPTCHA (Completed Automated Public Turing test to tell Computers and Humans Apart) boxes is annoying. It is also sometimes difficult to decipher the wavy text, leading to multiple attempts to prove yourself a flesh and blood human and not a robot. Well, good news—Google's reCAPTCHA, which is the most widely used CAPTCHA service on the service, is going invisible.

Google has been leading in this area for some time. Its No CAPTCHA reCAPTCHA implementation consists of a checkbox for users to click indicating "I'm not a robot." In some instances, users might be asked to click on a series of thumbnail images—for example, it might ask, "Click on the images containing a car." Easy stuff, but still an annoyance when trying to surf the web. That's about to change.

"Since the launch of No CAPTCHA reCAPTCHA, millions of internet users have been able to attest they are human with just a single click. Now we're taking it a step further and making it invisible. Human users will be let through without seeing the 'I'm not a robot' checkbox, while suspicious ones and bots still have to solve the challenges," Google stated in a blog post.

CAPTCHA schemes exist not to annoy users, but to protect websites again spam bots. Google does not say a whole lot about how it works, saying only that it uses an advanced risk analysis engine and adaptive CAPTCHAs to keep bots from sneaking in, while letting valid users through the gate. Rather than rely on distorted text, it considers the users entire engagement with CAPTCHA.

The interesting thing about reCAPTCHA is that when a user is tasked with picking out an image or passing some other test, Google uses that information to improve its other services.

"reCAPTCHA helps solve hard problems in artificial intelligence. High quality human labelled images are compiled into datasets that can be used to train machine learning systems. Research communities benefit from such efforts that help build the next generation of groundbreaking artificial intelligence solutions," Google explains.

It is not clear how switching to an invisible reCAPTCHA scheme might affect those types of side benefits.